The present invention relates to the control of an electric generator set including an engine and an alternator. In particular, the present invention relates to the control of an electric generator set that has a variable load at the output of the alternator.
Electric generator sets (or xe2x80x9cgensetsxe2x80x9d) are widely used to provide electric power. A genset typically includes an engine coupled to an alternator, which converts the rotational energy from the engine into electrical energy. The terminal voltage of a genset is proportional to both the magnetic flux density within the alternator, and the speed of the engine. The magnetic flux density is typically determined by controlling an armature voltage or field current on the alternator, while the speed of the engine is typically determined by an engine governor.
When a load is attached to the output terminals of the alternator or when an attached load increases in size, the speed of the engine tends to drop unless the engine governor appropriately adjusts the position of the throttle of the engine. In practice, the adding or increasing of a load does not adversely affect the performance of a genset if the load is only added gradually to the alternator or if the load is very small, since the engine governor is capable of effectively responding to the increased load. However, if a load is too quickly added to the alternator, particularly if the load is large, an excessive drop in the speed of the engine can occur. The engine governor is unable to open the throttle fast enough to maintain the engine""s speed. Because the speed of the engine drops excessively, the output voltage and frequency of the alternator also drop excessively.
Although it would be desirable if an engine governor was capable of opening a throttle at a faster rate in order to maintain an engine""s speed, mechanical time constraints inherent in conventional engine systems limit the rate at which a throttle can be opened.
Further, while certain prior art systems exist that maintain engine speed despite sudden increases in the load on the alternator, none of these prior art systems both (a) maintains the voltage output level of the alternator at the desired level and (b) applies to gensets in which the AC power output of the alternator is directly supplied to outside power lines or other loads without rectification or inversion. That is, certain prior art systems exist which maintain engine speed approximately constant by momentarily relaxing the armature voltage or field current when the load on the alternator suddenly increases. By relaxing the armature voltage or field current, the effective load on the engine is decreased, and consequently the speed of the engine does not decrease as much as it otherwise would. While an excessive drop in the engine speed is prevented by these systems, the output voltage of the alternator cannot remain at the desired level but rather must decrease because of the decrease in the armature voltage or field current.
Other prior art systems exist that prevent an excessive drop in the engine speed of a genset by causing the throttle of the engine to open rather than by relaxing the armature voltage or field current of the alternator. However, these prior art systems determine whether it is necessary to open the throttle of the engine by measuring DC power output of the genset. That is, these prior art systems apply only to gensets in which the AC power output from the alternators is rectified into DC power. Such gensets include rectifiers to convert the AC power into DC power, and must further include inverters to reconvert the DC power into AC power suitable for output to power lines and other AC loads. Thus, these prior art systems are not applicable to gensets in which the AC power output of the alternators is to be directly connected to power lines and other AC loads.
It would therefore be advantageous if a method and apparatus were developed for preventing or minimizing the decreases in the engine speed of a genset that occur when there are sudden load increases at the output of the alternator of the genset. It would additionally be advantageous if the operation of the method and apparatus did not negatively affect the output voltage and frequency of the alternator, and if the method and apparatus were applicable to gensets that were designed to directly supply AC power output from the alternators to power lines or other AC loads, without any intermediate rectification or inversion.
The present inventors have discovered that it is possible to counteract the tendency of the engine of a genset to slow down in response to an increased load on the alternator of the genset by causing the throttle to open up sooner than it otherwise would if only the engine governor were being utilized to control the throttle. The present inventors have further discovered that it is possible to determine when such action to open the throttle should be taken solely based upon information concerning the AC power output of the alternator of the genset, without rectification.
The present invention relates to a method of controlling a genset having an engine and an alternator in order to prevent an excessive change in a speed of the engine because of a sudden change in a load on the alternator. The method includes obtaining a first measured value of an actual AC output power of the alternator at a genset controller during a first time period, and obtaining a second measured value of the actual AC output power of the alternator at the genset controller during a second time period. The method additionally includes determining at the genset controller a first output power based upon at least the first measured value, and a second output power based upon at least the second measured value. The method further includes determining at the genset controller, based upon the first output power and the second output power, whether the actual AC output power has changed in an amount greater than a first threshold, and providing a first control signal from the genset controller to the genset causing a position of a throttle to be modified when it is determined that the actual AC output power has changed in an amount greater than the first threshold.
The present invention additionally relates to an apparatus for controlling a genset having an engine and an alternator in order to prevent an excessive change in a speed of the engine because of a sudden change in a load on the alternator. The apparatus includes a first input terminal configured to receive at least a first measured value and a second measured value of an actual AC output power of an alternator of the genset, and a processor coupled to the first input terminal. The processor is configured to determine a first output power and a second output power based upon at least the first measured value and at least the second measured value, respectively, and to determine, based upon the first output power and the second output power, whether the actual AC output power has changed in an amount greater than a first threshold. The apparatus further includes a first output terminal that is coupled to the processor and configured to provide a first output signal to the genset causing a position of a throttle on the genset to change when the processor determines that the actual AC output power of the alternator has changed in an amount greater than the first threshold.
The present invention additionally relates to an apparatus for converting mechanical energy into electrical energy. The apparatus includes a genset including an engine coupled to an alternator, and an engine control module coupled to the genset. The apparatus further includes a means for monitoring an actual AC output power of the alternator, for determining whether the actual AC output power has increased in an amount greater than a first threshold, and for providing a first signal to the engine control module in order to cause an opening of a throttle of the engine when it is determined that the actual AC output power has increased in an amount greater than the first threshold.